Ideas originating within the intellect, j from its very nature, rather than acquired through experience. Rationalistic philosophers have defended and empiricists have denied the existence of such ideas. Among the many think¬ers who have in one way or another referred to innate ideas, five are of major importance.

Plato (c. 427-347 B.C.) regarded certain ideas, such as jus¬tice or courage in ethics and equality in mathematics, as latent within the mind. These ideas, he maintained, could not be gained by generalization from particular instances. On the one hand, they exceed in logical purity and excel¬lence the actual course of events; and on the other hand, they are needed in order to enable men to know which of the many occurrences in the world around us are properly manifestations of these ideas. Borrowing the mythological language of the Pythagoreans, he then asserted that men have certain ideas before they are born and may recover knowledge of them by serious examination of what is in their own minds. His point was thus that men bring to the inter¬pretation of experience certain ideas which they could never have derived from the analysis of experience.

Rene Descartes (1596-1650) applied the theory of innate ideas to certain ultimate principles of scientific purport, such as that a cause must contain at least as much perfection as the effect it produces, that the essence of the mind is think¬ing and the essence of matter is extension, and, in general, that whatever we quite clearly and distincdy conceive must be true of the world around us.

John Locke (1632-1704) devoted the first book of his Essay Concerning Human Understanding to refuting the theory of innate ideas. All our ideas, he contended, come from experience. The mind is at birth a sheet of blank paper, and all ideas are derived from the original materials of experience, or from comparison, abstraction, or a combina¬tion of these materials.

Immanuel Kant (1724-1804) gave a new version of the theory of innate ideas. Experience, he held, is the joint prod¬uct of two diverse elements, the content given to the mind from without and the form which the mind imposes upon this content. The former element is factual and contingent: hence our ideas about it are acquired bit by bit from ex¬perience. The latter element is formal and necessary: hence our ideas about it, although they arise in us in the course of experience, are discovered to be universally valid for all pos¬sible, as well as actual, experience. These latter ideas have a validity and certainty which are due to the fact that they are based upon a priori requirements which mind imposes upon experience if experience is to occur at all.

Herbert Spencer (1820-1903) presented an attenuated theory of innate ideas by utilizing his favorite doctrine of evolution. All ideas, he argued, are acquired in the history of the development of the human race. But some ideas eventually become native to individuals because they become ingrained gradually in human nature.

The issue concerning innate ideas is not altogether a historical one; it is still under debate. No one would now seek to argue that people are born with ideas already consciously present in their minds: even Spencer’s mild version of this supposition has made few converts. The issue has become whether or not any of the ideas we have, irrespective of the occasions when they first appear in us, are such that they cannot be regarded as derived entirely from the analysis of experience, and whether or not such ideas, if there be any, then have a validity such that confirmation of them by experience is neither requisite nor relevant to our knowledge of their truth.